A robotic arm generally requires complex cable systems to, for example, distribute power to multiple motor-actuated joints or convey signals detected by electro-mechanical sensors placed in various locations within the joints. Robotic arms that include distributed control and vision systems require additional wiring, such as Ethernet, USB, or RS-232, to link to control nodes for serial communications. The cable systems passing through robotic arms must be capable of accommodating joint movements and various mechanical displacements yet remain resistant to mechanical wear.
Conventionally, a large robotic arm is centrally controlled and large bundles of cables are routed externally to the joints. This approach may avoid the design difficulties of accommodating cables internally in the space-constrained package of the joints, but requires large cable loops with support structures to accommodate the motion of the robotic arm. Additionally, the externally bundled cables risk snagging the cable on an external object during joint movement.
Another cable-management strategy utilizes internalized cable wiring; this is sometimes used for smaller arms intended for use in proximity to human operators. Typically, slip rings are used in small, compact robots to link wiring between flexible joints. Alternatively, a highly flexible cable can be routed through the joints. The highly flexible cables, however, must be rated for millions of flex cycles before they experience mechanical wear; cable wear may result in increased electrical noise or intermittent connections. In addition, approaches employing either the slip rings or the highly flexible cable are expensive and thereby increase system cost.
In still another approach, bundles of torsion-rated cables are employed and passed through the center of a robot joint in order to minimize displacement of the cables during joint movement. This approach, however, requires creation of internal spaces within the joints for the cable flexure. Additionally, large holes through the central axis of each joint are typically necessary to accommodate passage of the bundled cables and/or facilitate connection to different elements inside the joints; this approach thus typically requires more space in the joint and/or special joint configurations, thereby increasing system complexity and cost.
Consequently, there is a need for an approach to cable management that provides for connection among various elements associated with the robot joints without the need for extra space or expensive support components, while avoiding cable wear.